Minor changes from v7 based on feedback from Longman: ----------------------------------------------------- - Move __init functions from alternative.c to qspinlock_cna.h - Introduce enum for return values from cna_pre_scan(), for better readability. - Add/revise a few comments to improve readability. Summary ------- Lock throughput can be increased by handing a lock to a waiter on the same NUMA node as the lock holder, provided care is taken to avoid starvation of waiters on other NUMA nodes. This patch introduces CNA (compact NUMA-aware lock) as the slow path for qspinlock. It is enabled through a configuration option (NUMA_AWARE_SPINLOCKS). CNA is a NUMA-aware version of the MCS lock. Spinning threads are organized in two queues, a main queue for threads running on the same node as the current lock holder, and a secondary queue for threads running on other nodes. Threads store the ID of the node on which they are running in their queue nodes. After acquiring the MCS lock and before acquiring the spinlock, the lock holder scans the main queue looking for a thread running on the same node (pre-scan). If found (call it thread T), all threads in the main queue between the current lock holder and T are moved to the end of the secondary queue. If such T is not found, we make another scan of the main queue after acquiring the spinlock when unlocking the MCS lock (post-scan), starting at the node where pre-scan stopped. If both scans fail to find such T, the MCS lock is passed to the first thread in the secondary queue. If the secondary queue is empty, the MCS lock is passed to the next thread in the main queue. To avoid starvation of threads in the secondary queue, those threads are moved back to the head of the main queue after a certain number of intra-node lock hand-offs. More details are available at https://arxiv.org/abs/1810.05600. The series applies on top of v5.5.0-rc2, commit ea200dec51. Performance numbers are available in previous revisions of the series. Further comments are welcome and appreciated. Alex Kogan (5): locking/qspinlock: Rename mcs lock/unlock macros and make them more generic locking/qspinlock: Refactor the qspinlock slow path locking/qspinlock: Introduce CNA into the slow path of qspinlock locking/qspinlock: Introduce starvation avoidance into CNA locking/qspinlock: Introduce the shuffle reduction optimization into CNA .../admin-guide/kernel-parameters.txt | 18 + arch/arm/include/asm/mcs_spinlock.h | 6 +- arch/x86/Kconfig | 20 + arch/x86/include/asm/qspinlock.h | 4 + arch/x86/kernel/alternative.c | 4 + include/asm-generic/mcs_spinlock.h | 4 +- kernel/locking/mcs_spinlock.h | 20 +- kernel/locking/qspinlock.c | 82 +++- kernel/locking/qspinlock_cna.h | 400 ++++++++++++++++++ kernel/locking/qspinlock_paravirt.h | 2 +- 10 files changed, 537 insertions(+), 23 deletions(-) create mode 100644 kernel/locking/qspinlock_cna.h -- 2.21.0 (Apple Git-122.2)
